Exception thrown in NSOrderedSet generated accessors

Question

On my Lion app, I have this data model:

The relationship subitem

Answer 1

Received the same error, @LeeIII solution worked for me (thanks!). I suggest slightly modify it:

• use objective-c category to store the new method (so we wont lose our method if Item is generated again)
• check if we already have mutable set

Content of Item+category.m:

#import "Item+category.h"

@implementation Item (category)

- (void)addSubitemsObject:(SubItem *)value {
    if ([self.subitems isKindOfClass:[NSMutableOrderedSet class]]) {
        [(NSMutableOrderedSet *)self.subitems addObject:value];
    } else {
        NSMutableOrderedSet* tempSet = [NSMutableOrderedSet orderedSetWithOrderedSet:self.subitems];
        [tempSet addObject:value];
        self.subitems = tempSet;
    }
}

@end